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   "source": [
    "# Copyright 2014 Brett Slatkin, Pearson Education Inc.\n",
    "#\n",
    "# Licensed under the Apache License, Version 2.0 (the \"License\");\n",
    "# you may not use this file except in compliance with the License.\n",
    "# You may obtain a copy of the License at\n",
    "#\n",
    "#     http://www.apache.org/licenses/LICENSE-2.0\n",
    "#\n",
    "# Unless required by applicable law or agreed to in writing, software\n",
    "# distributed under the License is distributed on an \"AS IS\" BASIS,\n",
    "# WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.\n",
    "# See the License for the specific language governing permissions and\n",
    "# limitations under the License.\n",
    "\n",
    "# Preamble to mimick book environment\n",
    "import logging\n",
    "from pprint import pprint\n",
    "from sys import stdout as STDOUT"
   ]
  },
  {
   "cell_type": "code",
   "execution_count": 2,
   "metadata": {
    "collapsed": false
   },
   "outputs": [
    {
     "name": "stdout",
     "output_type": "stream",
     "text": [
      "['Plato', 'Socrates', 'Aristotle', 'Archimedes']\n"
     ]
    }
   ],
   "source": [
    "# Example 1\n",
    "names = ['Socrates', 'Archimedes', 'Plato', 'Aristotle']\n",
    "names.sort(key=lambda x: len(x))\n",
    "print(names)"
   ]
  },
  {
   "cell_type": "code",
   "execution_count": 3,
   "metadata": {
    "collapsed": true
   },
   "outputs": [],
   "source": [
    "# Example 2\n",
    "from collections import defaultdict\n",
    "\n",
    "def log_missing():\n",
    "    print('Key added')\n",
    "    return 0"
   ]
  },
  {
   "cell_type": "markdown",
   "metadata": {},
   "source": [
    "### We can pass function as an argument "
   ]
  },
  {
   "cell_type": "code",
   "execution_count": 4,
   "metadata": {
    "collapsed": false
   },
   "outputs": [
    {
     "name": "stdout",
     "output_type": "stream",
     "text": [
      "Before: {'green': 12, 'blue': 3}\n",
      "Key added\n",
      "Key added\n",
      "After:  {'red': 5, 'orange': 9, 'green': 12, 'blue': 20}\n"
     ]
    }
   ],
   "source": [
    "# Example 3\n",
    "current = {'green': 12, 'blue': 3}\n",
    "increments = [\n",
    "    ('red', 5),\n",
    "    ('blue', 17),\n",
    "    ('orange', 9),\n",
    "]\n",
    "result = defaultdict(log_missing, current)\n",
    "print('Before:', dict(result))\n",
    "for key, amount in increments:\n",
    "    result[key] += amount\n",
    "print('After: ', dict(result))"
   ]
  },
  {
   "cell_type": "code",
   "execution_count": 5,
   "metadata": {
    "collapsed": false
   },
   "outputs": [],
   "source": [
    "# Example 4\n",
    "def increment_with_report(current, increments):\n",
    "    added_count = 0\n",
    "\n",
    "    def missing():\n",
    "        nonlocal added_count  # Stateful closure\n",
    "        added_count += 1\n",
    "        return 0\n",
    "\n",
    "    result = defaultdict(missing, current)\n",
    "    for key, amount in increments:\n",
    "        result[key] += amount\n",
    "\n",
    "    return result, added_count"
   ]
  },
  {
   "cell_type": "code",
   "execution_count": 6,
   "metadata": {
    "collapsed": false
   },
   "outputs": [
    {
     "name": "stdout",
     "output_type": "stream",
     "text": [
      "defaultdict(<function increment_with_report.<locals>.missing at 0x103e7dd08>, {'red': 5, 'orange': 9, 'green': 12, 'blue': 20})\n"
     ]
    }
   ],
   "source": [
    "# Example 5\n",
    "result, count = increment_with_report(current, increments)\n",
    "assert count == 2\n",
    "print(result)"
   ]
  },
  {
   "cell_type": "code",
   "execution_count": 7,
   "metadata": {
    "collapsed": true
   },
   "outputs": [],
   "source": [
    "# Example 6\n",
    "class CountMissing(object):\n",
    "    def __init__(self):\n",
    "        self.added = 0\n",
    "\n",
    "    def missing(self):\n",
    "        self.added += 1\n",
    "        return 0"
   ]
  },
  {
   "cell_type": "code",
   "execution_count": 8,
   "metadata": {
    "collapsed": false
   },
   "outputs": [
    {
     "name": "stdout",
     "output_type": "stream",
     "text": [
      "defaultdict(<bound method CountMissing.missing of <__main__.CountMissing object at 0x103e8c550>>, {'red': 5, 'orange': 9, 'green': 12, 'blue': 20})\n"
     ]
    }
   ],
   "source": [
    "# Example 7\n",
    "counter = CountMissing()\n",
    "result = defaultdict(counter.missing, current)  # Method reference\n",
    "for key, amount in increments:\n",
    "    result[key] += amount\n",
    "assert counter.added == 2\n",
    "print(result)\n",
    "\n",
    "\n",
    "# Example 8\n",
    "class BetterCountMissing(object):\n",
    "    def __init__(self):\n",
    "        self.added = 0\n",
    "\n",
    "    def __call__(self):\n",
    "        self.added += 1\n",
    "        return 0\n",
    "\n",
    "counter = BetterCountMissing()\n",
    "counter()\n",
    "assert callable(counter)"
   ]
  },
  {
   "cell_type": "code",
   "execution_count": 9,
   "metadata": {
    "collapsed": false
   },
   "outputs": [
    {
     "name": "stdout",
     "output_type": "stream",
     "text": [
      "defaultdict(<__main__.BetterCountMissing object at 0x103e8ca58>, {'red': 5, 'orange': 9, 'green': 12, 'blue': 20})\n"
     ]
    }
   ],
   "source": [
    "# Example 9\n",
    "counter = BetterCountMissing()\n",
    "result = defaultdict(counter, current)  # Relies on __call__\n",
    "for key, amount in increments:\n",
    "    result[key] += amount\n",
    "assert counter.added == 2\n",
    "print(result)"
   ]
  }
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